Turning wine waste into value: A techno-economic and environmental study of phenolics, syngas and biochar production

Abstract

Grapes are one of the most important crops globally, but 30 % of their weight becomes waste in the wine industry. This work aims to valorise two of the most important wastes in this industry, grape marc and grape stalks, by extracting the total phenolic compounds (TPC) as well as biochar and syngas, through a pyrolysis process of the remaining organic biomass. From grape marc, 5.99 tonnes of phenolic compounds and 46.91 kg of biochar were obtained per batch, whereas for grape stalks, the TPC yield increased to 8.06 tonnes, while biochar production decreased to 27.89 tonnes per batch. To assess the environmental impacts of this biorefinery, the Life Cycle Assessment methodology was applied, revealing global warming impacts of 80.30 kg CO₂ eq and 102.07 kg CO₂ eq per kilogram of TPC for grape stalk (GS) and grape marc (GM), respectively, with steam production identified as the system’s main hotspot. The initial design results are not profitable, primarily due to high equipment costs, which significantly exceed the revenues from product sales and also lead to elevated annual manufacturing costs. However, the sensitivity analysis shows that adjusting the plant's construction and operating costs to values more in line with the literature leads to a significant increase in the internal rate of return, reaching up to 36.16 % in certain scenarios. Potential improvements to the plant should focus on changing the source of heat generation to cleaner energy sources, aiming for a transition towards more sustainable production.